The method described herein is applicable to the removal of metal from a hydrocarbon solution of metal alkaryl sulfonate. A typical hydrocarbon which is contaminated with such metal alkaryl sulfonates is petroleum crude oil.
Aqueous solutions containing metal alkaryl sulfonates are used in the enhanced oil recovery (EOR) of petroleum crude oil from subterranean formations. The petroleum crude oil is recovered concurrently with an aqueous phase and after the separation of the aqueous phase from the crude oil, a substantial amount of metal sulfonate remains in the crude oil portion. The crude oil may be contaminated with sulfonates in an amount from about 10 to 5000 parts per million by weight, or more. The metal alkaryl sulfonates are often referred to as surfactants. The metal which is associated with the sulfonate and which contaminates the recovered crude oil must be removed or substantially reduced before the crude oil undergoes any further refining and processing. The presence of metal in the crude oil during subsequent processing may cause corrosion, environmental pollution and/or hydrorefining catalyst poisoning. The class of sulfonates most useful in enhanced oil recovery applications is the sodium petroleum sulfonates. Any surfactant present in the produced oil will accompany that oil and will be processed in the refinery as part of the crude oil. Processing of EOR crude oil containing surfactants especially sodium petroleum sulfonates will be detrimental to the refinery catalyst by causing severe deactivation. It is believed that deactivation occurs from the deposition of the metal, and sodium in particular, of the surfactant on the surface of the catalyst which unfavorably alters the performance of the catalytic sites.
Since enhanced oil recovery is becoming widespread in the oil production industry, the problem of surfactant contaminated crude oil is well known. Candor compels the acknowledgement that those skilled in the art are working in many directions to solve the problem. For example, U.S. Pat. No. 4,274,943 (McClaflin) teaches a method for the removal of metal alkaryl sulfonates from a hydrocarbon solution threof which method comprises (a) contacting the hydrocarbon solution containing metal alkaryl sulfonates with an aqueous basic solution containing a "recovery" surfactant, (b) forming a hydrocarbon phase and an aqueous phase containing metal alkaryl sulfonates and (c) separating the hydrocarbon phase and the aqueous phase. U.S. Pat. No. 4,274,943 is one method which the prior art utilizes to separate or extract metal alkaryl sulfonates from recovered petroleum crude oil and is incorporated herein by reference thereto.
As hereinabove described, the inventor in U.S. Pat. No. 4,274,943 has chosen to remove the entire metal alkaryl sulfonate molecular component from the crude. In stark contrast, we have discovered a novel and effective method for the removal of the metal portion of the metal alkaryl sulfonate and substituting in place of the metal component a relatively innocuous substance to preserve the molecular integrity of the sulfonate. Since the metal is effectively removed from the crude oil, the possibility of catalyst deactivation resulting from the presence of a metal component and any other potential difficulties are alleviated. The method of the present invention will be described in detail hereinafter.